Self-oriented iron oxide nanorod array thin film for photoelectrochemical hydrogen production

In this work, iron films were deposited on fluorine-tin-oxide coated glass substrate using radio frequency sputtering. Self-oriented iron oxide nanorod array thin films were obtained by anodizing the sputtered films. Anodization was carried out in an ethylene glycol solution containing 0.1 M NH ₄F and various content of water. We studied the mechanism of anodization of iron thin films, and investigated the effects of some parameters on the properties of the iron oxide thin films. Nanorod-like structures were observed from cross-sectional field-emission scanning electron microscope images. The size of the pores between the nanorods varies from 48 to 140 nm. The pore size increases as the conductivity of the electrolyte was increased from 596 to 957 μS/cm by adjusting water content. The direct energy band gaps of the samples are found to vary from 1.95 to 2.2 eV. The flat-band potentials were obtained from Mott-Schottky analysis and found to be in the range of -0.7 V to -0.75 V. The maximum photocurrent density was 0.72 mA/cm ² with a bias voltage of 0.5 V (V vs. Ag/AgCl), under a 300 W xenon lamp system. Highlights: Properties of iron oxide thin films for solar water splitting were investigated. The self-oriented nanorod array films were obtained by anodizing iron films. Effects of anodization parameters were studied. Energy band gaps are found to vary from 1.95 to 2.2 eV from Mott-Schottky analysis. The maximum photocurrent density was 0.72 mA/cm ² with a bias voltage of 0.5 V.